Heat capacity anomalies in Fe-8 single crystal

A preliminary heat capacity study of Fe-8 molecules as a function of applie d magnetic field, temperature and measuring frequency is presented. The hea t capacity versus temperature curve shows in zero field several peaks betwe en 2 and 3 K. The anomalies shift to a lower temperature when a magnetic he ld is applied. With increasing field the peaks are smeared. No frequency de pendence could be established in the measured range of omega = 217-4440 Hz. We have also performed heat capacity measurements as a function of magneti c held at fixed temperature. Between 2 and 3 K a pattern of well developed peaks at discrete magnetic field values is observed. The pattern strongly c hanges in the small temperature range between 2.3 and 2.5 K. (C) 1999 Elsev ier Science B.V. All rights reserved.